This invention relates to a method for the manufacture or orthomethylated phenol compounds by the methylation of phenols having at least one ortho-hydrogen.
The orthomethylated phenol compounds which are produced by the method of this invention are useful as industrial raw materials. For example, 2,6-xylenol is a raw material for polyphenylene oxide and ortho-cresol is a raw material for agricultural pesticides and pharmaceutical products.
Methods which produce orthomethylated phenol compounds by the vapor-phase catalytic reaction of a phenol compounds with methanol and consequently methylating the orthoposition of phenol compounds have already been known to the art. A number of catalysts have been proposed for use in this reaction.
For example, the method of British Pat. No. 717,588 methylates ortho-cresol using metal oxide, particularly aluminum oxide, as a catalyst. Since the activity and the selectivity for the ortho-position are low, this method produces the orthomethylated compound (2,6-xylenol) in low yields. Moreover, the method produces by-products such as meta-methylated and para-methylated phenols.
Since it is extremely difficult to isolate 2,6-xylenol from the reaction mixture containing such by-products, this method is neither technically nor economically advantageous.
The method of U.S. Pat. No. 3,446,856 carries out the reaction using magnesium oxide as a catalyst at a very high temperature of 475.degree. to 600.degree. C. Thus, it has a disadvantage that the energy consumption is large and the catalytic activity-retaining property is poor.
Among the catalysts which have low reaction temperatures and, therefore, prove advantageous from the standpoint of energy consumption, those containing iron oxide have found recognition.
For example, Japanese Patent Publication No. 12610/1976 produces 2,6-xylenol by effecting the reaction at 350.degree. C. in the presence of a catalyst prepared from iron oxide and chromium oxide. This method, however, produces 2,6-xylenol in low yields.
Japanese Patent Publication No. 37944/1972 produces 2,6-xylenol by use of a catalyst composed of iron oxide and indium oxide in respective proportions such that the atomic ratio of indium to iron falls in the range of 9/1 to 1/9. Still, this method produces 2,6-xylenol in low yields and has a disadvantage that the proportion of the converted methanol which has been utilized effectively in the reaction with phenol and ortho-cresol to the whole converted methanol, namely the utilization ratio of methanol, is extremely low and the greater part of the converted methanol has just survived in a decomposed form.
The method of Japanese Patent Publication No. 1269/1977 (corresponding to U.S. Pat. No. 3,953,529, West German Pat. No. 2,428,056, and British Pat. No. 1,428,057) uses a catalyst composed of iron oxide, chromium oxide, and silicon oxide and that of Japanese Patent Publication No. 12692/1977 (corresponding to U.S. Pat. No. 4,024,195, West German Pat. No. 2,547,309, and British Pat. No. 1,507,478) uses a catalyst composed of iron oxide, chromium oxide, silicon oxide, and alkali metal compound respectively in the production of 2,6-xylenol. The inventors of this invention have reproduced these two catalysts by carefully following the disclosures and made studies thereon, to learn that although they are improved in activity and activity-retaining property over the other catalysts described above, they fall short of functioning satisfactorily.
The inventors, therefore, have continued extensive studies in search of a catalyst which exhibits high activity at a low reaction temperature enough for economy of energy consumption, excels in activity-retaining property, shows high ortho-position selectivity, and warrants high utilization ratio of methanol.
They have consequently found that the catalyst composed of iron oxide and indium oxide has, outside the range of percentage composition heretofore known to the art, a range of percentage composition (involving a smaller proportion of indium) in which the catalyst acquires higher activity, exhibits excellent ortho-position selectivity, and provides high utilization ratio of methanol.
A further study revealed, however, that the catalyst composed of iron oxide and indium oxide lost its catalytic activity rapidly. In other words, this catalyst has been confirmed to have a very poor activity-retaining property.